I am not familiar with Comcast's VOIP service. But when you buy another comparable VOIP gadget to replace Comcast's, but the problem is in Comcast's network infrastructure for supporting VOIP, you will probably see the same problem. It looks like the "ooma" is only a gadget that converts regular voice traffic signal (which uses PCM I think) to the VOIP packets. But how does your internet service provider (Comcast I presume) sends the VOIP packets to your receiver is out of ooma's control.

RE: My router has only 4 ports... to add 2 Ooma for 2 phone lines, I'll need 6 ports. Do I just plug the switch into the router then the 2 Ooma into the switch?

The best is to have a router which offer enough RJ45 ports. If you use a switch to share one of the ports on the router, there will be bandwidth contention. It may or may not be a bid deal. If you have 2 ooma devices hooked up to a switch, and from the switch to the router... then I suspect you may experience issues when both phones are used in a conversation. (Or maybe not. )

I assume you have a home/retail router (like a Linksys/Cisco WRT54G or newer model).

You ideally want only a switch connected to your router - no computers or any other devices. Let the router route internet traffic and handle DHCP only. Most retail or lower grade business routers don't have the CPU or onboard memory to handle throughput capacity of both switched and routed networking - meaning they can route WAN internet traffic to a LAN IP - OR - handle switching network traffic/bandwidth from one IP to the next on your LAN, but they can't do both very well.

Then run one cat5/6 cable from your router into your switch and then run all of your ancillary stuff off the switch. This will provide you much more even and consistant internet access as well as provide for much better throughput on the LAN (file sharing, computer-to-computer or NAS type stuff).

The reality is any router you have is going to be at least 100mbps capable, if not gigabit (1000mbps) capable and it is doubtful that you have access to anywhere near 100mbps on your home internet connection. People usually think that the one little wire going between the switch and the router will be the bottleneck - but that is not the case at all - it will actually be faster overall.

Your issue is you are either stressing the router past its limits - or your internet service provider is crappy.

sorry for the long response - short answer is buy a decent managed switch and you'll have no problems putting whatever you want on the switch.